In any welding process, the welder must consider the type of material being joined together. In many applications, much of the material comprising the electrode combines with the weldment components affecting its properties. It can be important to select an electrode that corresponds to the base material properties. Accordingly, electrodes are categorized by their properties, primarily tensile strength. Other electrode classifications relate to the types and amounts of metal alloys incorporated into the electrode, as well as the welding position in which the electrode is capable of making a satisfactory weld.
Electrodes also introduce impurities or other undesirable substances into the weld joint. Some electrodes are constructed to contain moisture, which may come in the form of a cellulose coating. Moisture bolsters the arc force and increases weld penetration. However, hydrogen from the moisture is also introduced into the weld joint. For high tensile strength materials, the hydrogen acts like a small fissure leading to cracks in the weld. Pressurized containers are especially vulnerable to these effects. Pipelines are just one example of where it is critical to minimize the amounts of hydrogen added to the weld joint.
New welders, using a stick electrode, are taught to strike an arc by “scratching” the surface of the weld metal. This motion initiates the arc while avoiding “sticking” where the electrode fuses to the weldment. The scratching technique elongates the arc until the welder can move the electrode in closer to the work piece. This draws in air, which adds porosity to the weld joint.